During the transition from home to college, students exhibit a dramatic increase in substance use, high- risk HIV/sex-risk behaviors, and associated harms. Prevalence of alcohol and marijuana use, and of non- medical prescription stimulant and painkiller use, is high among college students, who represent 40% of our young adult population. Parents remain influential with young adult students, but the mechanisms of risk and protection at this developmental stage in the family domain are not well understood. Our overarching goal is to reduce the incidence of death, injury, sexual assault, and academic failure related to substance use and related risk behaviors among college students. Our immediate objective is to test the efficacy of a preventive intervention for parents as their students transition to college. The rationale for this project, an interactive parent handbook, is that it wll provide college administrators with a new, low-cost tool that will (a) significantly reduce risk behaviors, injuries, sexual assault, and deaths; and (b) increase academic success among first- year students. The handbook, Letting Go and Staying Connected, is interactive, theoretically guided, and developmentally targeted. It will provide parents with evidence-based parenting skills during a transitional period in which they often seek guidance and support. Preliminary results from a pilot study indicate that students whose parents participated in the intervention were significantly less likely to use substances and experience harms during their first semester than were control students. We will randomly assign parent-student dyads (450 dyads per cohort; two cohorts) to one of three groups: Handbook, Handbook Plus (an innovative booster condition in which some Handbook parents receive tailored text messages), and Control. All participants will complete a baseline survey during summer before the first year of college. Handbook parents then receive the mailed handbook; Handbook Plus parents also receive booster messages in fall semester. Follow-up surveys will occur once a semester for two years. Our aims are 1) to test the efficacy of the Handbook: we expect that students of parents receiving the handbook will engage in less substance use and fewer high-risk sex behaviors than control students; 2) to evaluate mediating and moderating factors: our hypothesized model specifies that parent behaviors will mediate associations between Handbook use and student outcomes; and 3) to identify specific attributes of parent-student communication (e.g., content; tone; timing) that predict risk behaviors. The project will allow us to test protective effects of specific aspects of parenting behaviors, and results will extend our limited knowledge about malleable risk and protective factors in the family domain for this developmental period. Additionally, the project will take place in Washington, a state where the purchase, possession, and use of marijuana have recently been legalized, providing timely information about effects of parent communication specifically about marijuana. In sum the project has practical, scientific, and policy significance.